Because flight recorders must survive the extreme conditions caused by disastrous airplane crashes, the crash survivable memory unit within the flight recorder requires extreme mechanical robustness, along with the ability to absorb a large quantity of thermal energy in a short time period. To withstand the extreme conditions, crash survivable memory units are insulated from the heat by brittle insulating materials and relatively uncompressible heat absorbing materials. Generally, the insulating material surrounds a layer of heat absorbing material, and the heat absorbing material surrounds a data storage device. Because the insulating material and heat absorbing material is either brittle or uncompressible, to protect the crash survivable memory, the enclosure is generally constructed from heavy gauge hardened steel so that the enclosure experiences as little deformation as possible.
Generally, an optimization process is used when designing the steel enclosure, the insulating material and the heat absorbing material to reduce the total enclosed volume and weight of the enclosure while still protecting against the extreme conditions of an aircraft crash. However, optimization of the enclosure geometry for structural robustness and practical limitations on the dimensions of the data storage device lead to uneven distribution of insulating and/or heat absorbing material. Further, the resultant crash survivable memory unit accounts for more than 70% of the total weight of a flight recorder with the steel enclosure accounting for approximately 65% of the weight of the crash survivable memory unit.